Self-descriptiveness asks whether the interface explains itself: what it shows, what can be done, and what will happen. A measure relates correct user understanding to the screens and users studied. A self-descriptive interface lets a user act without documentation. The measure is about comprehension, so it needs a user and a question: what does this screen tell you, what happens if you press this, what is this value. The population of screens should include the ones where a mistake is costly. The measure is cheap to collect with a comprehension test and expensive to fake, which makes it a good candidate for a regular check.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.